The present invention relates to electrostatic dust filters, and more particularly to fabric filters for removing dust particles or other particulate matter from a stream of air or other gas.
Conventional fabric dust filters consisting essentially of a layer of cloth, or other textile fabric, are very efficient dust collecting devices. The effectiveness of these devices, however, is not primarily due to the fabric filtering element itself but results from the layer of dust which collects on the fabric. This layer of dust provides a very effective filtering action but it tends to build up into a substantially impervious layer which results in excessive pressure drop across the filter. This is highly undesirable because of the excessive amount of power required to force a given flow of gas through the filter and necessitates frequent cleaning or replacement of the filter element.
In my copending application Ser. No. 381,781, filed July 23, 1973, now Pat. No. 3,910,779, issued Oct. 7, 1975, there is disclosed and claimed an electrostatic dust filter in which the dust deposits in a relatively porous layer so as to maintain a low pressure drop across the filter. This result is obtained by electrically charging the dust particles and maintaining an electric field at the surface of the fabric filter element so that the dust is deposited on the filter element in the electric field. The slight surface irregularities of the filter tend to concentrate the electric field and the charged dust particles follow the field so that they tend to deposit on these irregularities. This further concentrates the field and causes the dust to deposit in closely-spaced columns or pyramids so that the layer of dust remains relatively porous. A very effective filtering action with low pressure drop is obtained in this way but a relatively complicated and expensive construction is required for the filter itself to charge the dust particles in the desired manner while limiting the resulting space charge, and to maintain the required electric field at the surface of the filter elements.